DNA Polymerase alpha is essential for intracellular amplification of hepatitis B virus covalently closed circular DNA. 2019

Liudi Tang, and Muhammad Sheraz, and Michael McGrane, and Jinhong Chang, and Ju-Tao Guo
Microbiology and Immunology Graduate Program, Drexel University College of Medicine, Philadelphia, PA, United States of America.

Persistent hepatitis B virus (HBV) infection relies on the establishment and maintenance of covalently closed circular (ccc) DNA, a 3.2 kb episome that serves as a viral transcription template, in the nucleus of an infected hepatocyte. Although evidence suggests that cccDNA is the repair product of nucleocapsid associated relaxed circular (rc) DNA, the cellular DNA polymerases involving in repairing the discontinuity in both strands of rcDNA as well as the underlying mechanism remain to be fully understood. Taking a chemical genetics approach, we found that DNA polymerase alpha (Pol α) is essential for cccDNA intracellular amplification, a genome recycling pathway that maintains a stable cccDNA pool in infected hepatocytes. Specifically, inhibition of Pol α by small molecule inhibitors aphidicolin or CD437 as well as silencing of Pol α expression by siRNA led to suppression of cccDNA amplification in human hepatoma cells. CRISPR-Cas9 knock-in of a CD437-resistant mutation into Pol α genes completely abolished the effect of CD437 on cccDNA formation, indicating that CD437 directly targets Pol α to disrupt cccDNA biosynthesis. Mechanistically, Pol α is recruited to HBV rcDNA and required for the generation of minus strand covalently closed circular rcDNA, suggesting that Pol α is involved in the repair of the minus strand DNA nick in cccDNA synthesis. Our study thus reveals that the distinct host DNA polymerases are hijacked by HBV to support the biosynthesis of cccDNA from intracellular amplification pathway compared to that from de novo viral infection, which requires Pol κ and Pol λ.

UI MeSH Term Description Entries
D004256 DNA Polymerase I A DNA-dependent DNA polymerase characterized in prokaryotes and may be present in higher organisms. It has both 3'-5' and 5'-3' exonuclease activity, but cannot use native double-stranded DNA as template-primer. It is not inhibited by sulfhydryl reagents and is active in both DNA synthesis and repair. DNA Polymerase alpha,DNA-Dependent DNA Polymerase I,Klenow Fragment,DNA Pol I,DNA Dependent DNA Polymerase I,Polymerase alpha, DNA
D004270 DNA, Circular Any of the covalently closed DNA molecules found in bacteria, many viruses, mitochondria, plastids, and plasmids. Small, polydisperse circular DNA's have also been observed in a number of eukaryotic organisms and are suggested to have homology with chromosomal DNA and the capacity to be inserted into, and excised from, chromosomal DNA. It is a fragment of DNA formed by a process of looping out and deletion, containing a constant region of the mu heavy chain and the 3'-part of the mu switch region. Circular DNA is a normal product of rearrangement among gene segments encoding the variable regions of immunoglobulin light and heavy chains, as well as the T-cell receptor. (Riger et al., Glossary of Genetics, 5th ed & Segen, Dictionary of Modern Medicine, 1992) Circular DNA,Circular DNAs,DNAs, Circular
D004279 DNA, Viral Deoxyribonucleic acid that makes up the genetic material of viruses. Viral DNA
D006515 Hepatitis B virus The type species of the genus ORTHOHEPADNAVIRUS which causes human HEPATITIS B and is also apparently a causal agent in human HEPATOCELLULAR CARCINOMA. The Dane particle is an intact hepatitis virion, named after its discoverer. Non-infectious spherical and tubular particles are also seen in the serum. Dane Particle,Hepatitis Virus, Homologous Serum,B virus, Hepatitis,Hepatitis B viruses,Particle, Dane,viruses, Hepatitis B
D006801 Humans Members of the species Homo sapiens. Homo sapiens,Man (Taxonomy),Human,Man, Modern,Modern Man
D014771 Virion The infective system of a virus, composed of the viral genome, a protein core, and a protein coat called a capsid, which may be naked or enclosed in a lipoprotein envelope called the peplos. Virus Particle,Viral Particle,Viral Particles,Particle, Viral,Particle, Virus,Particles, Viral,Particles, Virus,Virions,Virus Particles
D014779 Virus Replication The process of intracellular viral multiplication, consisting of the synthesis of PROTEINS; NUCLEIC ACIDS; and sometimes LIPIDS, and their assembly into a new infectious particle. Viral Replication,Replication, Viral,Replication, Virus,Replications, Viral,Replications, Virus,Viral Replications,Virus Replications
D056945 Hep G2 Cells A human liver tumor cell line used to study a variety of liver-specific metabolic functions. Cell Line, Hep G2,Cell Line, Hepatoblastoma G2,Hep G2 Cell Line,HepG2 Cells,Hepatoblastoma G2 Cell Line,Cell, Hep G2,Cell, HepG2,Cells, Hep G2,Cells, HepG2,Hep G2 Cell,HepG2 Cell
D019694 Hepatitis B, Chronic INFLAMMATION of the LIVER in humans caused by HEPATITIS B VIRUS lasting six months or more. It is primarily transmitted by parenteral exposure, such as transfusion of contaminated blood or blood products, but can also be transmitted via sexual or intimate personal contact. Chronic Hepatitis B,Chronic Hepatitis B Virus Infection,Hepatitis B Virus Infection, Chronic
D022781 Hepatocytes The main structural component of the LIVER. They are specialized EPITHELIAL CELLS that are organized into interconnected plates called lobules. Hepatic Cells,Cell, Hepatic,Cells, Hepatic,Hepatic Cell,Hepatocyte

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